1. Field of the Invention
The present invention relates to an image inspection apparatus, an image inspection method, and an image recording apparatus, and particularly relates to an image inspection apparatus and an image inspection method which inspect a printed image by using a captured image obtained by capturing an image of a printed material, and an image recording apparatus including the image inspection apparatus.
2. Description of the Background Art
A mode of performing overprinting by using a pre-printed paper, such as a slip paper and a detailed statement paper, on which a frame line and/or a ruled line is printed in advance, has been widely used so far.
For example, FIG. 6 shows an exemplary case where overprinting is performed on a pre-printed paper having a frame line and a ruled line printed thereon. The part (a) of FIG. 6 shows a pre-printed paper PP having a frame line CL and a ruled line RL printed thereon, and the part (b) of FIG. 6 shows an exemplary case where overprinting has been performed within the frame line CL and above the ruled line RL.
In recent years, there has been demanded not only simple printing such as overprinting a character, a barcode, and the like, on a paper having a ruled line and/or a frame line, but also highly flexible printing such as overprinting a multi-valued image exemplified by a photograph or an illustration on a pre-printed paper having a multi-valued image exemplified by a background or a pattern
For example, the part (a) of FIG. 7 shows a pre-printed paper PP1 on which a ruled line RL, a frame line CL, and a background image within the frame line CL are printed, and the part (b) of FIG. 7 shows an exemplary case where overprinting has been performed within the frame line CL and above the ruled line RL.
In order to inspect a performance level of a result of such overprinting on the pre-printed paper, a method of capturing an image of the overprinted printing paper and inspecting the captured image is adopted. However, the captured image includes both a pre-printed element and an overprinted element, which causes a significant problem in an inspection process.
For example, when additionally-recorded data indicating the overprinted element and a captured image are compared with each other, the pre-printed element included in the captured image is a factor of an erroneous detection, which deteriorates an inspection accuracy.
FIG. 8 schematically shows such a case. The part (a) of FIG. 8 shows a captured image obtained by capturing an image of a printing paper on which overprinting is performed within the frame line CL and above the ruled line RL, and the part (b) of FIG. 8 shows additionally-recorded data for overprinting. When inspection is performed by comparing the captured image and the additionally-recorded data with each other, as shown in the part (c) of FIG. 8, the overprinted element included in the captured image data is not detected as a lack because the overprinted element coincides with the additionally-recorded data, but the frame line CL and the ruled line RL which are the pre-printed element included in the pre-printed paper PP are detected as a lack, a stain, or the like, because the pre-printed element does not coincide with the additionally-recorded data.
Therefore, it is necessary to reduce influence of the pre-printed element included in the captured image in some way.
To address the problem, for example, Japanese Patent No. 412736 discloses inspecting various printed materials after performing thereon an invalidation process in which a pre-printed element included in a captured image is substantially invalidated by using, as mask data, pre-printed element information which is prepared in advance.
However, the invalidation process is a mask process in which a mask image is prepared by setting a region where the pre-printed element exists to be 0 and a region where the pre-printed element does not exist to be 1, and a logical multiplication (AND operation) of the mask image and the captured image is performed. This method excludes all of regions where the pre-printed element exists from an inspection object. Thus, when there is a region where the overprinted element, a stain, a lack, or the like, overlaps the pre-printed element, such a region cannot be inspected, either. This raises a significant problem particularly when a pre-printed paper includes a pre-printed element such as a tint and a pattern as a background.
FIG. 9 schematically shows such a case. The part (a) of FIG. 9 shows a captured image of the pre-printed paper PP1 on which the ruled line RL, the frame line CL, and the background image within the frame line CL are printed, and the part (b) of FIG. 9 shows a mask image in which a region where the pre-printed element exists is masked based on the captured image of the pre-printed paper PP1. In the mask image, a region of the pre-printed element corresponding to the region within the frame line CL is a mask region M1, and a region of the pre-printed element corresponding to the ruled line RL is a mask region M2.
The part (c) of FIG. 9 shows a captured image obtained by capturing an image of the overprinted printing paper on which overprinting has been performed within the frame line CL and above the ruled line RL. The part (d) of FIG. 9 shows a result of the mask process being performed on the captured image by using the mask image shown in the part (b) of FIG. 9. In an example shown in the part (d) of FIG. 9, the mask region M1 excludes the region within the frame line CL from an inspection object, to make it impossible to inspect the overprinted element existing within the frame line CL.